Serbia's prime minister has condemned the "brutal treatment" of migrants by Hungarian police and warned the neighbouring country not to fire tear gas onto its territory again.

Aleksandar Vucic, speaking from the US while on an official visit, said he would raise the issue in a meeting Wednesday with US Secretary of State John Kerry.

Mr Vucic also said there must be an EU response to clashes between migrants and Hungarian police, who used tear gas, pepper spray and water cannons against hundreds of people at the Hungary-Serbia border.

Serbian doctors say two people have been seriously injured and between 200 and 300 have sought medical help after Hungarian police used tear gas and water cannons.

Dr Margit Pajor from the medical centre in Kanjiza, near the border, said that most of the migrants suffered cuts, bruises and burns or eye problems caused by tear gas.

She says that "they were lining up so we wash their eyes or put bandages".

She says two people have been sent to a nearby hospital, one of them with a serious head injury.